A natural knee unit functions on many levels, often times being involuntarily controlled by a person without deliberate thought. Prosthetic knees require conscious effort on the part of the amputee. As the natural knee possesses a multitude a simultaneous characteristics in one package, each prosthetic knee focuses and a handful of functions and attributes. The prosthetist and amputee must consider the advantages and disadvantages different prosthetic knee designs when designing the above knee prosthesis.
Each prosthetic knee design targets a body-weight class, amputation level, and activity level. Activity levels, or functional levels, are sometimes referred to as ‘K Levels’:
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K0 : This functional level is only used with an amputee who has no ability or potential to use a prosthesis to walk or transfer safely with or without assistance. In this case, a prosthesis would not enhance the person’s quality of life.
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K1 : In this case, the amputee must have the ability or the potential to use a prosthesis for walking or transferring with or without assistance. This person mainly walks indoors for very short distances and requires a high level of security. The amputee would have the ability or potential for walking only on level surfaces at a single cadence, or speed.
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K2 : Here, the amputee must have the ability or the potential to walk over low level barriers, such as curbs, stairs, or uneven surfaces. This is typical of the limited outdoor walker.
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K3 : This functional level applies to an amputee who has the ability or the potential to walk at various speeds. This person would be able to cross most environmental barriers and may have vocational, therapeutic, or exercise requirements that require a higher functioning prosthesis. This person is able to walk actively outdoors, unrestricted.
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K4 : This functional level is typical of any athlete, children, or extremely active individuals. This type of amputee exceeds basic abilities, experiences high stress when walking, and requires high energy levels.
Manufacturers define which knee is appropriate for which functional level and insurance companies are also provided with this information. Many insurance companies, including any that follow Medicare guidelines, will only provide benefit coverage for a knee if the patient is documented to be of the appropriate functional level for that prosthetic knee.
In order to find the assigned target functional level for a prosthetic knee, the part number for the specific knee unit must be available. The manufacturer publishes these target functional levels, and the prosthetist should also be familiar with this information.
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